1. Field of the Invention
The present invention relates to a control apparatus for actuating vehicle safety devices such as an air-bag, a safety belt tightening device and the like in a motor vehicle.
2. Description of the Prior Art
For ensuring the safety of motor vehicle passengers, there have been developed various vehicle safety devices such as air-bag, the safety belt tightening devices and the like. For these devices to work effectively, it is necessary to detect when a collision has occurred as soon as possible in the prior art and there have been proposed various devices for meeting requirement.
For example, Japanese Patent Application Public Disclosure No. Sho 49-55031 discloses a conventional device in which the output from a deceleration sensor is integrated when the output level of the deceleration sensor exceeds a predetermined level to obtain information concerning the vehicle speed thereafter and it is determined that the vehicle has collided with an obstruction when the decrease in the vehicle speed reaches a prescribed level. Thus, in the conventional device, the operation necessary for ensuring the safety of the operator and passengers of the motor vehicle is actuated in response to the detection of collision.
It is generally said that a safety device can effectively protect the car occupants only if it can limit the maximum displacement of the occupants, especially their heads, to within fifteen to twenty centimeters at the time of collision. Accordingly, considering that it takes approximately thirty milliseconds from the time of the actuation of an electrically fired actuator for, for example, an air-bag, to the time of the completion of the expansion thereof, it is necessary to decide whether or not a collision has occurred within twenty to twenty-five milliseconds after it happens. The conventional control apparatus of this kind is of course designed in consideration of this fact to perform the appropriate triggering operation for the electrically or mechanically fired actuator.
However, actual collisions can occur in many ways that make it very difficult for the conventional control apparatus to assuredly detect the occurrence of the collision within the required period of time. The difficulty arises because, in the conventional apparatus the discrimination as to whether a collision has occurred is based on whether the integrated value of the deceleration of the motor vehicle has reached a predetermined level. However, collisions are not always simple events, for example, the motor vehicle may firstly be accelerated forward in a rear-end collision and be decelerated when it collides with another vehicle in front. Therefore, in the conventional apparatus wherein the occurrence of a collision is discriminated by the fact that the degree of deceleration of the vehicle has reached the predetermined level, it follows that there will sometimes be a long interval between the time of the collision condition and the time the degree of the deceleration of the vehicle reaches the predetermined level. This is particularly true where the vehicle is momentarily accelerated at the occurrence of the collision. Accordingly, in such a case, there is no assurance of being able to detect the occurrence of the collision within the predetermined time period required for assuring the safety of the car occupants.